While the effort to reduce the pattern rule is in rapid progress to meet the recent demand for higher integration density and operating speed of LSIs, the photolithography is on widespread use. The photolithography has the essential limit of resolution determined by the wavelength of a light source. One micropatterning approach to go beyond the limit of resolution is by combining ArF excimer laser immersion lithography with double patterning. One typical version of double patterning is litho-etch-litho-etch (LELE) process involving forming a pattern via exposure, transferring the pattern to a hard mask on a substrate by etching, effecting second exposure at a half-pitch shifted position, and etching the hard mask. This process has the problem of misalignment between two exposures or overlay error. Another version of double patterning is self-aligned double patterning (SADP) process involving the steps of transferring a resist pattern to a hard mask, growing a film on opposite sides of hard mask features, and leaving sidewalls of film for thereby doubling pattern size. The SADP process needs exposure only once and mitigates the problem of overlay error. To simplify the process, a modified version of the SADP process of forming a silicon oxide film on sidewalls of resist pattern features as developed rather than sidewalls of hard mask features for thereby doubling pattern size is also proposed. Since the SADP process is successful in reducing the pitch of line pattern to half, the pitch can be reduced to ¼ by repeating the SADP process twice.
Not only shrinking of line patterns, but also shrinking of hole patterns is necessary. Unless the hole pattern is shrunk, shrinkage over the entire chip is incomplete. One known method of shrinking a hole pattern is RELACS® method described in JP-A H10-73927. This method intends to reduce the size of a hole pattern by coating a resist pattern as developed with a water-soluble material containing a crosslinker, and baking the coating to form a crosslinked layer on the resist surface for causing the resist pattern to be thickened. JP-A 2008-275995 describes a water-soluble shrink material comprising an amino-containing polymer or polyamine, which bonds to the resist surface via neutralization reaction with carboxyl groups on the resist surface, for thereby thickening the resist film. It is also proposed in Proc. SPIE Vol. 8323 p83230W-1 (2012) to shrink a hole pattern by utilizing the direct self-assembly (DSA) of a block copolymer.
Shrinkage by the RELACS® method has the problem that since a crosslinker becomes active with an acid catalyst within resist, the size of holes is non-uniform after shrinkage if acid diffusion is non-uniform. In the shrink method based on neutralization and bonding of water-soluble amino polymer, the pattern is thickened as direct reflection of irregularities on the resist surface so that dimensional variations of the resist pattern as developed and dimensional variations after shrinkage are identical. There is another problem that the polymer bonds not only to the resist surface, but also to the substrate surface. The shrink method utilizing the DSA function of a block copolymer has advantages including an increased amount of shrinkage and a minimal dimensional variation after shrinkage, but some problems. Namely, if the DSA is applied to holes of different size, shrinkage cannot be induced for those holes of the size that causes a contradictory assembly of block copolymer. If the DSA is applied to a trench pattern, shape deformation becomes a problem, for example, a plurality of hole patterns are formed.
There is a need for a shrink agent which bonds to only the surface of a resist pattern as developed, but not to the substrate surface, can shrink a trench or hole pattern without changing the shape of the resist pattern, and improve the dimensional variation and edge roughness (LWR) of the resist pattern.